How the octagon pool volume calculator works
Area is 2 times 1 plus the square root of 2, multiplied by the side length squared. That works out to roughly 4.828 times the side squared.
Multiply the area by the water depth for cubic feet. Octagon pools normally have a flat floor, so one depth reading is enough.
The formula
Volume = 2 x (1 + square root of 2) x side squared x depth
Measure: Side length, depth.
Worked example
A pool with 6 foot sides has an area of 4.828 x 36, which is 173.8 square feet.
At 4 feet of water that is 695.3 cubic feet, about 5,201 gallons or 19,690 litres.
Tips before you measure
Measure one flat panel, not the distance across the pool. Using the width across will more than double your answer.
If the sides are not equal, average them or treat the pool as freeform for a safer estimate.
Octagon pool volume FAQs
Do I measure across the pool or one side?
One flat side. The formula multiplies that side length up to the full eight sided area.
Does this work for a wooden octagon pool?
Yes. Measure the inside of the liner at the water line rather than the outside of the timber.
What if two sides are longer?
Elongated octagons are closer to a rectangle with clipped corners, so use the Grecian calculator.
Other pool shapes
Not quite the right outline? The main pool volume calculator covers all 20 shapes with the same units and formulas.